Method for inhibiting deterioration of high temperature fluidity of high-aluminum steel covering slag

Abstract

This invention relates to the field of continuous casting technology in steelmaking, and particularly to a method for suppressing the deterioration of high-temperature fluidity of protective slag in high-alumina steel. The method comprises the following effective component percentage content in the protective slag: CaO: 2-4%, CaF2: 34.84-39.94%, NaCl: 7.8-9.3%, Na2O+K2O < 0.5%, Li2O: 1-5%, Al2O3: < 1%, MgO: < 1.5%, C: 3-5%. The mass percentage content of SiO2 should satisfy the formula: where W... SiO2 W CaF2 W CaO The percentages of SiO2, CaF2, and CaO in the protective slag are, in %; W [Al] The percentage of [Al] in the cast steel is expressed as %. This system ensures stable high-temperature flow characteristics of the protective slag when casting high-aluminum steel with an aluminum content of 2-7%, solving the problems of billet quality and smooth continuous casting caused by changes in the viscosity of the protective slag.

Description

Technical Field

[0001] This invention relates to the field of steelmaking continuous casting technology, and in particular to a method for suppressing the deterioration of high-alumina steel protective slag at high temperatures. Background Technology

[0002] Mold flux, as an indispensable functional material in continuous casting, plays a crucial role in the smooth operation of continuous casting and the quality of the cast billet. The physical properties of the mold flux include melting point, melting rate, viscosity, and crystallization temperature. Among these, the viscosity of the mold flux directly determines the uniformity and thickness of the slag film in the gap between the cast billet and the crystallizer wall. Excessive viscosity reduces the fluidity of the mold flux, resulting in less liquid slag flowing into the gap between the primary billet shell and the water-cooled crystallizer wall, and a thinner slag film, affecting heat transfer and lubrication performance. Conversely, excessively low viscosity results in strong fluidity, leading to more liquid slag flowing into the gap between the primary billet shell and the water-cooled crystallizer wall, resulting in a thicker and more uneven slag film, which also affects heat transfer and lubrication performance, thus impacting the quality of the cast billet.

[0003] When molten steel contains a high content of Al, the SiO2 in the protective slag reacts with it, resulting in Al2O3 replacing SiO2. This increases the alkalinity of the slag, and some Al2O3 acts as a network former, causing the network structure to aggregate. Consequently, the viscosity of the protective slag increases sharply, the fluidity of the molten slag deteriorates, and the casting process is affected. Current research on protective slags for high-alumina steel mainly focuses on two aspects: First, the use of low-reactivity CaO-Al2O3-based protective slags. The purpose of these slags is to achieve good casting conditions by inhibiting the reaction between the steel and slag, but this approach does not consider the changes in the physical properties of the protective slag after the adsorption of Al2O3 inclusions, and therefore has not been widely adopted. Second, the low-alkalinity CaO-SiO2-based protective slags widely used by steel mills. These slags perform well in the early stages of casting, but as the casting time increases, the viscosity of the protective slag increases, preventing it from flowing properly into the slag channel. This severely deteriorates the lubrication of the cast billet, affecting its smooth casting process. There are currently no reports on research into stabilizing the high-temperature fluidity of protective slag. Therefore, there is an urgent need to develop a method to suppress the deterioration of the high-temperature fluidity of high-alumina steel protective slag and solve the problem of sudden changes in the high-temperature viscosity of protective slag caused by steel slag reaction.

[0004] This invention provides a method for suppressing the deterioration of the high-temperature fluidity of the protective slag for high-alumina steel. By using this method, the problem of a significant increase in the viscosity of the protective slag at high temperatures (1200-1300℃) after the steel slag reaction is effectively solved. This ensures good high-temperature fluidity of the protective slag, thereby enabling the high-alumina steel to achieve smooth continuous casting. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by providing a method for suppressing the deterioration of the high-temperature fluidity of high-alumina steel protective slag.

[0006] The objective of this invention is achieved as follows: a method for suppressing the deterioration of high-alumina steel protective slag at high temperatures, wherein the effective components of the protective slag have the following percentage content: CaO: 2-4%, CaF2: 34.84-39.94%, NaCl: 7.8-9.3%, Na2O+K2O < 0.5%, Li2O: 1-5%, Al2O3: < 1%, MgO: < 1.5%, C: 3-5%, with the remainder being SiO2 and unavoidable impurities.

[0007] The mass percentage content of SiO2 satisfies the formula: Among them, W SiO2 The mass percentage of SiO2 in the protective slag, %; W CaF2 The percentage of CaF2 in the protective slag, expressed as %; W CaO The percentage of CaO in the protective slag, expressed as %; W [Al] The percentage of Al in the cast steel (%).

[0008] The aluminum content in the high-aluminum steel is 2% to 7%.

[0009] The high-temperature fluidity, or high-temperature fluid stability, refers to the viscosity fluctuation of the protective slag before and after the steel slag reaction within 0.06 Pa·s in the temperature range of 1200-1300℃.

[0010] The beneficial effects of the present invention are: (1) The present invention uses CaF2 as the main base material, which effectively stabilizes the high-temperature fluidity of the protective slag.

[0011] (2) Based on the content of Al element in molten steel, the present invention accurately gives the mass percentage content ratio of SiO2 in protective slag, so that the viscosity of the protective slag of CaF2-SiO2 system after Al2O3 replaces SiO2 and the CaF2-Al2O3 system after the same replacement is consistent.

[0012] (3) NaCl was used to replace Na2O in the traditional protective slag, which greatly improved the stability of the protective slag during high-temperature flow. Attached Figure Description

[0013] The present invention will now be further described with reference to the accompanying drawings.

[0014] Figure 1 This is a graph showing the changes in the high-temperature fluidity of the protective slag before and after the reaction of steel slag under traditional technology; Figure 2 This is a graph showing the change in the high-temperature fluidity of the protective slag before and after the steel slag reaction under the technology of this invention. Detailed Implementation

[0015] This invention addresses the problem of viscosity deterioration in protective slag used for high-alumina steel due to shortcomings in existing technologies, proposing a method to suppress the deterioration of high-temperature fluidity in protective slag for high-alumina steel. This method effectively solves the problem of abrupt viscosity changes in protective slag at high temperatures under existing technological conditions by adjusting the slag system composition, using CaF2 as the base material, adding NaCl and Li2O as fluxes, and quantitatively incorporating SiO2 according to the [Al] element in high-alumina steel. The technical solution of the invention is as follows.

[0016] 1. The percentage content of effective components in the protective slag is as follows: CaO: 2-4%, CaF2: 34.84-39.94%, NaCl: 7.8-9.3%, Na2O+K2O <0.5%, Li2O: 1-5%, Al2O3: <1%, MgO: <1.5%, C: 3-5%. The remainder is SiO2 and unavoidable impurities.

[0017] 2. Furthermore, the mass percentage content of SiO2 is closely related to the [Al] element in high-alumina steel. The higher the Al content, the lower the effective basicity of the protective slag required, and the higher the corresponding mass percentage content of SiO2. This ensures sufficient SiO2 to compensate for the viscosity of the protective slag after the steel slag reaction, thereby achieving the goal of stabilizing the high-temperature fluidity of the protective slag. The mass percentage content of SiO2 should satisfy the formula: Among them, W SiO2 The mass percentage of SiO2 in the protective slag, %; W CaF2 The percentage of CaF2 in the protective slag, expressed as %; W CaO The percentage of CaO in the protective slag, expressed as %; W [Al] The percentage (%) of [Al] in the cast steel.

[0018] 3. Furthermore, the high-alumina steel is continuously cast. The aluminum content in the steel is 2% to 7%.

[0019] 4. Further, the physical properties of high-alumina steel protective slag are as follows: melting point 950-1060℃, viscosity at 1300℃: 0.1-0.23 Pa.s.

[0020] 5. Furthermore, the high-temperature flow stability mentioned here refers to the viscosity fluctuation of the protective slag before and after the steel slag reaction (the redox reaction between Al in high-alumina steel and SiO2 in the protective slag) within 0.06 Pa·s in the temperature range of 1200-1300℃.

[0021] 6. This invention uses a high content of CaF2 as the base material because CaF2 does not react with Al in steel, and its fluoride ions can effectively reduce the melting point and viscosity of the protective slag at high temperatures. When the CaF2 content is higher than 32%, the viscosity of the protective slag no longer decreases significantly, but remains at a relatively stable value. Moreover, at high temperatures (1200-1300℃), the viscosity of the CaF2-SiO2 system and the CaF2-Al2O3 system protective slag with the same substitution is almost the same. Therefore, even if Al2O3 replaces SiO2 in the protective slag, the high-temperature viscosity of the protective slag remains relatively stable.

[0022] 7. This invention uses NaCl to replace Na2O in traditional protective slag. On one hand, NaCl does not react with [Al] in the steel to form steel slag, exhibiting excellent chemical stability. On the other hand, NaCl's solubility in water at room temperature is higher than that of sodium carbonate, and it does not react. Adding NaCl mainly adjusts the melting point and viscosity of the protective slag based on CaF2.

[0023] Example

[0024] High-alumina steel with a cast aluminum content of 2.3%

[0025] 1. The percentage content of effective components in the protective slag is as follows: CaO: 3.2%, CaF2: 37.2%, NaCl: 8.1%, Na2O+K2O=0.15%, Li2O: 4.1%, Al2O3: 0.8%, MgO: 1.2%, C: 3.5%.

[0026] 2. The mass percentage content of SiO2 should meet the following formula:

[0027] 3. The prepared protective slag has a melting point of 1023℃ and a viscosity of 0.19 Pa·s at 1300℃.

[0028] High-alumina steel with a cast aluminum content of 6.5%

[0029] (1) The percentage content of effective components of protective slag is as follows: CaO: 2.0%, CaF2: 35.1%, NaCl: 8.5%, Na2O+K2O=0.15%, Li2O: 4.5%, Al2O3: 0.8%, MgO: 1.1%, C: 3.5%.

[0030] (2) The mass percentage content of SiO2 should meet the following formula:

[0031] (3) The melting point of the prepared protective slag is 980℃, and the viscosity at 1300℃ is 0.13 Pa·s.

[0032] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for suppressing the deterioration of high-alumina steel protective slag at high temperatures, characterized in that: The percentage content of effective components in the protective slag is as follows: CaO: 2~4%, CaF2: 34.84~39.94%, NaCl: 7.8~9.3%, Na2O+K2O<0.5%, Li2O: 1~5%, Al2O3: <1%, MgO: <1.5%, C: 3-5%, with the remainder being SiO2 and unavoidable impurities; The mass percentage content of SiO2 satisfies the formula: Among them, W SiO2 The percentage of SiO2 in the protective slag, %; W CaF2 The percentage of CaF2 in the protective slag (%); W CaO The percentage of CaO in the protective slag (%); W [Al] The percentage of Al by mass in the cast steel, % The aluminum content in the high-aluminum steel is 2% to 7%. The high-temperature fluidity, or high-temperature fluid stability, refers to the viscosity fluctuation of the protective slag before and after the steel slag reaction within 0.06 Pa·s in the temperature range of 1200-1300℃.

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